Dissolution kinetics of fluorapatite in the hydrochloric acid solution

A thermochemical study of hydrochloric acid attack of synthetic fluorapatite was performed by a DRC. The calculated thermogenesis curves show one peak. The plot of the heat quantity as a function of the dissolved mass undergoes only one straight segment, and the thermogenesis curves present a single peak, suggesting the occurrence of a one-step dissolution process. The dissolution kinetics was examined according to the heterogeneous reaction models and showed that the dissolution is controlled by the product layer diffusion process with a reaction rate expressed by the following semiempirical equation; (left[ {1 + 2(1 - X) - 3(1 - X)^{{frac{2}{3}}} } right] = 3195 times 10^{ - 2} C^{0.145} left( {frac{S}{L}} right)^{ - 0.628} e^{{ - frac{2600}{text T}}} t). The activation energy was determined as 21.6 ± 1.5 kJ mol^?1